1. Technical Field
The present invention relates to a technology that measures the strength of a magnetic field.
2. Related Art
As the technology that measures the strength of a magnetic field, an atom magnetization sensor that uses an electronic spin polarization of alkali metal gas is suggested. When a pump light of a circular polarized light is irradiated with respect to a cell in which an alkali metal vapor is present and a probe light of the straight polarized light passes through the cell, the polarized light surface of the probe light rotates according to the strength of the magnetic field that is applied to the cell. Thus, the strength of the magnetic field is measured by detecting a polarization rotation angle of the probe light.
A technology has been developed such that when the strength of a magnetic field is measured, a magnetic field gradient is measured using two cells that are disposed at different positions to each other from an object being measured, because magnetic fields that are caused by terrestrial magnetism, electric noise or the like in addition to the magnetic field of the object being measured may also get measured (for example, JP-A-2009-162554).
According to the technology described in JP-A-2009-162554, even if the magnetic field that is generated from the object being measured has low strength, there is an advantage in that the magnetic field can be precisely measured. However, the measuring precision may be low when the strength of the magnetic field and the polarization rotation angle of the probe light are not in a proportionate relation. Given that an increase in the strength of the magnetic field and the maintenance of the proportionate relation cannot be performed simultaneously, the strength of all the magnetic fields in a measuring environment needs to be restrained so as not to exceed any upper limit of the strength and the measurable strength of the magnetic field of the object being measured is greatly restricted. Therefore, there is a need to use an expensive magnetic shield.
Also, the probe light is absorbed by the influence of the alkali metal vapor of the cell through which the probe light passes. There is a case where if the strength of the probe light is different when passing through the cell, the amount of change in the polarization rotation angle may be different even in a magnetic field of the same strength, so that when the absorption amount becomes large, the relation of the polarization rotation angle with respect to the magnetic field in the two cells causes them to differ from each other and the magnetic field gradient cannot be precisely measured.